Color Genetics of Gotland Sheep in North America

by Franna Pitt, PhD

Copyright, 2007

What ColorPattern is my Gotland Sheep?

As I've discussed, all sheep are genetically either black or brown - at the
B locus. The expression of that color can be modified by genes at the pattern
locus, which is called A, and regulated by a gene at the Extension locus, E.
Sheep can have color from the two different pigments (eumelanin and phaeomelanin)
in a number of different "patterns". Basically, anytime you see a
regular distribution of light and dark color in a sheep, it probably is due
to the A locus. Unlike B - where there are only two possibilities, at A, there
are at least 6 possibilities and many people believe there are a lot of patterns
and variations that are as yet unidentified. It is the most complex of the sheep
color genes.

White

The first pattern allele is the most simple and also the dominant one - and
that is White. White is a "pattern" known as AWt for white/tan because
the tan pigment (phaeomelanin) is interchangeable and often intermixed with
white on sheep. In the sheep world, white is the most common color - now you
know it is the most common "pattern". Even though a sheep might be
black (eumelanin) at the B locus, if it carries even one copy of the AWt allele
at the A locus, it will be white! The AWt allele has the effect of inhibiting
one of the metabolic steps in eumelanin synthesis, so although the sheep has
the gene to make the black pigment, the AWt gene stops it from doing so.

We know the Gotland sheep pattern is NOT AWt. (hint - Gotlands are grey, not
white)

Solid

The second pattern is the recessive one - Solid color. A whole, solid color
is recessive to all of the other sheep patterns. The lambs on the previous page
are Solid patterned. It is known as Aa, and since it is the most recessive pattern,
any solid sheep must be homozygous Aa/Aa. (We haven't gotten to the Gotland
pattern yet....)

With just these two alleles at A, you can predict several genotypes. A solid,
brown sheep as shown in the photo in the previous section must be Aa/Aa Bb/Bb,
the most recessive genotype. A solid, black sheep has two options Aa/Aa BB/BB
or Aa/Aa BB/Bb. A white sheep only has to have one copy of the AWt allele, and
that white hides other patterns and the basic color. Now you know how colors
and patterns can hide in flocks of white sheep for many generations until the
right (or wrong!!!) combination of sire and dam brings out the phenotype. Here
are some possible genotypes for a white sheep:

Below is a Punnett square showing how two white sheep can produce white, black
and brown offspring:

Sire (AWt/Aa BB/Bb), Dam (AWt/Aa Bb/Bb)

Sire (below) Dam (right)

AWt, Bb

AWt, Bb

Aa, Bb

Aa, Bb

AWt, BB

AWt/AWt BB/Bb

AWt/AWt BB/Bb

AWt/Aa BB/Bb

AWt/Aa BB/Bb

AWt, Bb

AWt/AWt Bb/Bb

AWt/AWt Bb/Bb

AWt/Aa Bb/Bb

AWt/Aa Bb/Bb

Aa, BB

Aa/AWt BB/Bb

Aa/AWt BB/Bb

Aa/Aa BB/Bb

Aa/Aa BB/Bb

Aa, Bb

Aa/AWt Bb/Bb

Aa/AWt Bb/Bb

Aa/Aa Bb/Bb

Aa/Aa Bb/Bb

One eighth (2 squares of 16) of the theoretical offspring are brown, one eighth
are black. The other 75% are white, some of which are homozygous white (25%),
the others are heterozygous white (50%). They all vary in whether they are brown
or black, or black carrying brown. This is a lot of variation with just two
gene loci! This square hints at just how complex, yet predictable, color genetics
can be.

Now, the patterns get interesting - and more complex. The other pattern alleles
at A control the distribution of white, black, brown and tan fibers. They are
recessive to white, and dominant to solid. They can coexist
with each other... very interesting!

Badger-Faced

The sheep below is a purebred Shetland ewe. Her basic color is BROWN. (Note
there is no black on her - not her nose or hooves or lips or eyes.) She has
a pattern of light and dark, brown and tan, especially on her face and legs.
This pattern is known as "badger-face" or in Shetland-ese "katmoget",
and is noted as Ab.

Badger-faced sheep have this pattern of light and dark on their faces and legs,
plus they have dark bellies usually with a dark stripe running down their throat
and up to their tail. Their upper bodies are light colored, either fawn (in
brown based sheep) or grey (in black based sheep). The tan areas (forehead,
cheeks, knees, inside legs) can be very rich or almost washed out white. The
Grey Katmoget Shetland ewe below has very rich color, shown best right after
shearing and before any sunbleaching takes place.

Mouflon

Next pattern! This one is often called "reverse badgerface"
since the sheep are dark on top and light underneath. It is also known as "Mouflon"
or "Gulmoget" in Shetland-ese, and sometimes "black and tan",
and is noted as At. Mouflon sheep have a distinctive facial pattern. Note the
light teardrop/eye splashes and underjaw on the Shetland ram lamb below. The
light neck, chest and underbody, and tan lower legs are also typical of this
pattern. What basic color is this ram? Brown? Right! Mouflon sheep can also
be black based. Can they be white with this pattern? Nooooo, white is dominant,
so if a sheep has a gene for white they are solid white. If a sheep is white
AND mouflon (AWtAt) they look solid white. (This photo was taken just
after this ram broke a horn - poor little guy!)

Here's another question - can a sheep be Badger faced and Mouflon??? Well,
yes. The two patterns can co-exist. It is called co-dominance. The genetic notation
is AbAt. The ram below is At/Ab (or Ab/At - they mean the same thing). He looks
like he has a regular pattern, but it's not quite Badgerface, and not quite
Mouflon, kind of "muddy" and indistinct. All of his offspring are
either badgerface or mouflon. Pretty neat, right? Well, not if you're breeding
Gotlands!

Blue or English Blue

This next pattern is commonly found in the luster longwool breeds.
It can be fairly subtle or very distinct. The "English Blue" pattern
(Abl) is evidenced by a characteristic light teardrop on their faces as the
Wensleydale/Gotland lamb below shows. They can also have the light muzzle and
grey fleece in lighter or darker shades as they mature.

The 50% Gotland lamb below also shows the characteristic English
Blue markings. It already shows shading characteristic of both the Abl pattern
(light sides and tail) and of the Agg pattern (light neck ring and suger lips).
Some English Blue sheep are very light in color as adults. Their faces are still
dark with the characteristic teardrops. These two examples are BLACK based.
Though not as common, English blue sheep can also be BROWN based.

As with the co-dominance of Mouflon and Badgerface, English Blue can co-exist
with Mouflon or Badgerface. Can all three coexist? Noooooo, each sheep only
gets TWO genes for pattern from its parents - one from Mom and one from Dad.
So, Ab/At, Ab/Abl, At/Abl are all possible combinations. I'll bet it is difficult
to tell by looking at a sheep if it is At/Abl! The At would probably overlay/wash
out the Abl enough that Abl would not be distinct enough to identify. By the
way, a sheep can also be homozygous (two copies of the same gene) for each of
these patterns - At/At, Ab/Ab or Abl/Abl. The offspring of each of these homozygous
sheep will be the same pattern as they are (unless they get a white pattern
gene that covers up everything!)

Grey and Gotland Grey

The LAST pattern gene I'm going to address is (finally!) the one of interest
to Gotland breeders. This one is called "grey" - what else??? It is
known as Ag. There are some who believe Gotlands might have their very own
pattern, designated Agg. So far, at least, the existance of Agg has not
been proven. I am going to use it. If you don't believe in Agg, just think "Ag"
wherever I write Agg. Ag (or Agg) is dominant to the solid pattern and recessive
to the white pattern. It is co-dominant with Ab, At, and Abl.

Ag (or Agg) has the effect of interspercing white fibers in the fleece as the
animal matures. Typically, the lambs are born solid black (or brown) with characteristic
white "sugar lips", and wisps of white inside their ears and groin.
The half Gotland-half Finn lamb below has classic "sugar lips". She
was even into the sugar with her nose! Ag and Agg lambs start turning grey dramatically
within a few weeks of birth. It is as if a switch were flipped - and the new
fleece comes in grey all at once. If they are still solid black (or brown) by
the time they're 8 to 12 weeks old, they're probably NOT Ag or Agg.

Sometimes Ag grey lambs can be quite wild in their mix of color, especially
in Shetlands. This Shetland ewe lamb below turned grey all over her body as
she matured - her head and legs stayed black.

As with all of the other patterns, "grey" can be black
based or brown based. Brown based, grey patterned sheep are often called "grey-brown"
or if they're Shetlands, they're called "musket". The Shetland lamb
below is part way through her transformation from dark lamb fleece to light
adult fleece. Notice that although her face and legs stay dark, the wooly areas
of her head are light.

An adult Agg sheep has a blend of white and black fibers that
make the sheep look "grey". Whitehall Daniel, the beautiful Gotland
ram below is one of the UK Gotlands who is being used in the North American
Gotland upbreeding program.

There have been Shetland sheep identified as solid grey
in color - not a mix of black and white fibers. Let's hope we don't have to
deal with those genetics, too! A great information site for all things Shetland,
including color genetics, is the "Shetland
Sheep Information Site".

What might an Agg/Ab sheep look like? The sheep in the photo below,
courtesy of Tongue River Icelandic Sheep, has a very ghostly look. Notice the
characteristic badgerface patterning to the head, and the rich tan on the legs.
As an adult, this sheep will probably have little of the dark neck/chest and
groin stripe left. (This is a purebred Icelandic sheep, so would be Ag/Ab, not
Agg/Ab.)

The next lamb is a half Gotland-half Icelandic sheep. Though more
difficult to see, this lamb is Agg/Ab. It is also spotted - another set
of genes that I'll discuss next. The white head and leg spots cover up some
of the katmoget markings. Enough markings are visible to positively identify
the Ab in this lamb, especially note the rich tan on her face and legs that
is characteristic of the badgerface pattern. Since the sire was Gotland - he
contributed Agg, the other half of this lamb's pattern genetic code.

Those are the 6 (or 7 if you're counting Agg) patterns that should
be important to the Gotland upbreeding program. To recap: